This invention relates to a direct memory access controller. More particularly, it relates to a technique which is effective when a direct memory access controller is utilized in a multi-microcomputer system.
A direct memory access controller transfers large amounts of data between a peripheral device such as floppy disk device and a RAM (random access memory) device or the like at high speed without the intervention of a microprocessor. Such direct memory access controllers are described in, for example, "HITACHI MICROCOMPUTER DATA BOOK 8/16-BIT MICROCOMPUTER PERIPHERAL LSI's" issued in September 1985 by Hitachi, Ltd., p. 168-p. 180 (for 8 bits) and p. 389 (for 16 bits).
In, for example, a multi-microcomputer system wherein an I/O subsystem (microcomputer system) such as graphic engine board is added to a main microcomputer system in order to enhance a system performance, it becomes necessary to transfer data between a RAM and a peripheral device across the two systems. The prior-art direct memory access controller as mentioned above, however, can only transfer data between a peripheral device and a RAM within a single microcomputer system. This has led to a problem. The data transfer between the RAM and the peripheral device cannot be carried out across the two systems.